Switched-tank DC transformer and voltage ratio switching method thereof

ABSTRACT

A switched-tank DC transformer and a voltage ratio switching method thereof are provided. The switched-tank DC transformer includes an input terminal, an output terminal, 2n inverting switches, 2n rectifying switches, 2n−2 clamping switches, n resonance tanks and n−1 support capacitors. The inverting switches are serially connected in sequence. There is an inverting node between every two neighboring inverting switches. A terminal of the rectifying switch is connected with a rectifying node. A terminal of the two clamping switch is electrically connected with a clamping node. The resonance tank is electrically connected between the inverting node and the rectifying node. The support capacitor is electrically connected between the inverting node and the clamping node. Every support capacitor and every resonance tank is switchable to be in a normal state or a voltage ratio switching state, thus a voltage ratio of the switched-tank DC transformer is allowed to vary correspondingly.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to China Patent Application No.201811338938.9, filed on Nov. 12, 2018, the entire content of which isincorporated herein by reference for all purposes.

FIELD OF THE DISCLOSURE

The present disclosure relates to a switched-tank DC transformer, andmore particularly to a switched-tank DC transformer and a voltage ratioswitching method thereof.

BACKGROUND OF THE DISCLOSURE

For ensuring the performance of the efficiency and quality of supplyingpower, the voltage regulator module (VRM) with intermediate busarchitecture (IBA) is usually utilized for transforming the power. Theintermediate bus architecture includes an intermediate bus transformer.Generally, the conventional intermediate bus transformer is alow-frequency switching DC transformer or a full-bridge LLC circuit. Thelow-frequency switching DC transformer regulates the output voltage bychanging the duty ratio, thus the adjustable output voltage is achieved.The full-bridge LLC circuit can achieve zero-voltage switching (ZVS)over the full range. Therefore, by controlling the switching frequencyto equal the resonance frequency of the tank of the full-bridge LLCcircuit, the voltage ratio is ensured to be the same at different loads,and a high efficiency of power transformation is achieved.

However, due to the high voltage ratio of the low-frequency switching DCtransformer, the efficiency of power transformation thereof is low. Inaddition, due to the fixed voltage ratio of the full-bridge LLC circuit,the output voltage thereof is not adjustable. Consequently, neither thelow-frequency switching DC transformer nor the full-bridge LLC circuitis able to achieve the high efficiency as well as the adjustable outputvoltage.

Therefore, there is a need of providing a switched-tank DC transformerand a voltage ratio switching method thereof in order to overcome theabove drawbacks.

SUMMARY OF THE DISCLOSURE

An object of the present disclosure provides a switched-tank DCtransformer and a voltage ratio switching method thereof. In theswitched-tank DC transformer, every support capacitor and everyresonance tank is switchable to be in a normal state or a voltage ratioswitching state. Accordingly, the voltage ratio of the switched-tank DCtransformer is changed at will. When the input voltage varies in a widerange, the range of the output voltage can be limited by adjusting thevoltage ratio of the switched-tank DC transformer. Therefore, both thehigh efficiency of power transformation and the adjustable outputvoltage are achieved. Moreover, with regard to the voltage regulatormodule including the switched-tank DC transformer, the efficiency andquality of supplying power thereof are enhanced.

In accordance with an aspect of the present disclosure, there isprovided a switched-tank DC transformer. The switched-tank DCtransformer includes an input terminal, an output terminal, 2n invertingswitches, 2n rectifying switches, 2n−2 clamping switches, n resonancetanks and n−1 support capacitors. The 2n inverting switches are seriallyconnected in sequence and form n inverting half-bridge circuits, where nis an integer larger than or equal to 2. The first inverting switch iselectrically connected with the output terminal, the (2n)th invertingswitch is electrically connected with the input terminal, there is aninverting node between every two neighboring inverting switches, the(2i−1)th inverting node is between the (2i)th inverting switch and the(2i−1)th inverting switch, and i is an integer larger than or equal to 2and smaller than or equal to n. The 2n rectifying switches form nrectifying half-bridge circuits sequentially. Each of the n rectifyinghalf-bridge circuits includes two rectifying switches serially connectedwith each other, one terminal of both the two rectifying switches areelectrically connected with a rectifying node, the other terminal of thetwo rectifying switches are electrically connected with a groundterminal and the output terminal respectively, and the (i)th rectifyingnode is between the (2i)th rectifying switch and the (2i−1)th rectifyingswitch. The 2n−2 clamping switches form n−1 clamping half-bridgecircuits sequentially. Each of the n−1 clamping half-bridge circuitsincludes two clamping switches serially connected with each other, oneterminal of both the two clamping switches are electrically connectedwith a clamping node, the other terminal of the two clamping switchesare electrically connected with the ground terminal and the outputterminal respectively, and the (i−1)th clamping node is between the(2i−2)th clamping switch and the (2i−3)th clamping switch. The resonancetank is electrically connected between the corresponding inverting nodeand the corresponding rectifying node, and the (i)th resonance tank iselectrically connected between the (2i−1)th inverting node and the (i)threctifying node. The support capacitor is electrically connected betweenthe corresponding inverting node and the corresponding clamping node,and the (i−1)th support capacitor is electrically connected between the(2i−2)th inverting node and the (i−1)th clamping node. Each of the n−1support capacitors is switchable to be in a normal state or a voltageratio switching state, and each of the n resonance tanks is switchableto be in the normal state or the voltage ratio switching state, thus avoltage ratio of the switched-tank DC transformer is allowed to varybetween 2 and 2n. When the (i−1)th support capacitor is in the normalstate, the (i−1)th clamping node is electrically connected with theground terminal and the output terminal by turns. When the (i−1)thsupport capacitor is in the voltage ratio switching state, the (i−1)thclamping node is kept constantly in an open-circuit condition, the(2i)th inverting switch or the (2i−2)th inverting switch is keptconstantly in an ON state, the (2i−1)th inverting switch or the (2i−3)thinverting switch is kept constantly in the ON state. When the (i)thresonance tank is in the normal state, the (i)th rectifying node iselectrically connected with the output terminal and the ground terminalby turns. When the (i)th resonance tank is in the voltage ratioswitching state, the (i)th rectifying node is kept constantly in theopen-circuit condition, the (2i+1)th inverting switch or the (2i−1)thinverting switch is kept constantly in the ON state, the (2i)thinverting switch or the (2i−2)th inverting switch is kept constantly inthe ON state.

In accordance with another aspect of the present disclosure, there isprovided a voltage ratio switching method of a switched-tank DCtransformer. The switched-tank DC transformer includes an inputterminal, an output terminal, 2n inverting switches, 2n rectifyingswitches, 2n−2 clamping switches, n resonance tanks and n−1 supportcapacitors, where n is an integer larger than or equal to 2. The 2ninverting switches are serially connected in sequence and form ninverting half-bridge circuits, the first inverting switch iselectrically connected with the output terminal, the (2n)th invertingswitch is electrically connected with the input terminal, there is aninverting node between every two neighboring inverting switches, the(2i−1)th inverting node is between the (2i)th inverting switch and the(2i−1)th inverting switch, and i is an integer larger than or equal to 2and smaller than or equal to n. The 2n rectifying switches form nrectifying half-bridge circuits sequentially, each of the n rectifyinghalf-bridge circuits includes two rectifying switches serially connectedwith each other, one terminal of both the two rectifying switches areelectrically connected with a rectifying node, the other terminal of thetwo rectifying switches are electrically connected with a groundterminal and the output terminal respectively, and the (i)th rectifyingnode is between the (2i)th rectifying switch and the (2i−1)th rectifyingswitch. The 2n−2 clamping switches form n−1 clamping half-bridgecircuits sequentially, each of the n−1 clamping half-bridge circuitsincludes two clamping switches serially connected with each other, oneterminal of both the two clamping switches are electrically connectedwith a clamping node, the other terminal of the two clamping switchesare electrically connected with the ground terminal and the outputterminal respectively, and the (i−1)th clamping node is between the(2i−2)th clamping switch and the (2i−3)th clamping switch. The resonancetank is electrically connected between the corresponding inverting nodeand the corresponding rectifying node, and the (i)th resonance tank iselectrically connected between the (2i−1)th inverting node and the (i)threctifying node. The support capacitor is electrically connected betweenthe corresponding inverting node and the corresponding clamping node,and the (i−1)th support capacitor is electrically connected between the(2i−2)th inverting node and the (i−1)th clamping node. The voltage ratioswitching method controls every support capacitor to be switchably in anormal state or a voltage ratio switching state. The voltage ratioswitching method controls every resonance tank to be switchably in thenormal state or the voltage ratio switching state. The voltage ratioswitching method allows a voltage ratio of the switched-tank DCtransformer to vary between 2 and 2n. The voltage ratio switching methodincludes: (a) controlling the (i−1)th support capacitor to be in thenormal state, namely controlling the (i−1)th clamping node toelectrically connect the ground terminal and the output terminal byturns; (b) controlling the (i−1)th support capacitor to be in thevoltage ratio switching state, namely controlling the (i−1)th clampingnode to be constantly in an open-circuit condition, controlling the(2i)th inverting switch or the (2i−2)th inverting switch to beconstantly in an ON state, and controlling the (2i−1)th inverting switchor the (2i−3)th inverting switch to be constantly in the ON state; (c)controlling the (i)th resonance tank to be in the normal state, namelycontrolling the (i)th rectifying node to electrically connect the outputterminal and the ground terminal by turns; and (d) controlling the (i)thresonance tank to be in the voltage ratio switching state, namelycontrolling the (i)th rectifying node to be constantly in theopen-circuit condition, controlling the (2i+1)th inverting switch or the(2i−1)th inverting switch to be constantly in the ON state, andcontrolling the (2i)th inverting switch or the (2i−2)th inverting switchto be constantly in the ON state.

The above contents of the present disclosure will become more readilyapparent to those ordinarily skilled in the art after reviewing thefollowing detailed description and accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram illustrating a switched-tank DCtransformer according to an embodiment of the present disclosure;

FIG. 2A is a schematic circuit diagram illustrating the switched-tank DCtransformer of FIG. 1 with n equal to 2;

FIGS. 2B and 2C are schematic diagrams showing the different switchconditions of the switched-tank DC transformer of FIG. 2A;

FIG. 3A is a schematic circuit diagram illustrating the switched-tank DCtransformer of FIG. 2A, wherein the support capacitor is in a firstvoltage ratio switching state, and the resonance tanks are in a normalstate;

FIGS. 3B and 3C are schematic diagrams showing the different switchconditions of the switched-tank DC transformer of FIG. 3A;

FIG. 4A is a schematic circuit diagram illustrating the switched-tank DCtransformer of FIG. 2A, wherein the support capacitor is in a secondvoltage ratio switching state, and the resonance tanks are in the normalstate;

FIGS. 4B and 4C are schematic diagrams showing the different switchconditions of the switched-tank DC transformer of FIG. 4A;

FIG. 5A is a schematic circuit diagram illustrating the switched-tank DCtransformer of FIG. 2A, wherein the support capacitor is in the firstvoltage ratio switching state, the first resonance tank is in the normalstate, and the second resonance tank is in the second voltage ratioswitching state;

FIGS. 5B and 5C are schematic diagrams showing the different switchconditions of the switched-tank DC transformer of FIG. 5A; and

FIG. 6 is a flowchart illustrating a voltage ratio switching methodaccording an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present disclosure will now be described more specifically withreference to the following embodiments. It is to be noted that thefollowing descriptions of preferred embodiments of this disclosure arepresented herein for purpose of illustration and description only. It isnot intended to be exhaustive or to be limited to the precise formdisclosed.

FIG. 1 is a schematic circuit diagram illustrating a switched-tank DCtransformer according to an embodiment of the present disclosure. Asshown in FIG. 1, the switched-tank DC transformer 1 includes an inputterminal 11, an output terminal 12, 2 n inverting switches (T₁, T₂ toT_(2n)), 2n rectifying switches (D₁, D₂ to D_(2n)), 2n−2 clampingswitches (S₁, S₂ to S_(2n−2)), n resonance tanks (RT₁, RT₂ to RT_(n))and n−1 support capacitors (C₁, C₂ to C_(n-1)), where n is an integerlarger than or equal to 2. There are an input voltage and an outputvoltage on the input terminal 11 and the output terminal 12respectively. The ratio of the input voltage to the output voltage isthe voltage ratio of the switched-tank DC transformer 1.

The 2n inverting switches T₁, T₂ to T_(2n) are serially connected insequence and form n inverting half-bridge circuits. The first invertingswitch T₁ is electrically connected with the output terminal 12, and the(2n)th inverting switch T_(2n) is electrically connected with the inputterminal 11. There is an inverting node (M₁, M₂ to M_(2n−1)) betweenevery two neighboring inverting switches (T₁, T₂ to T_(2n)). The firstinverting node M₁ is between the first inverting switch T₁ and thesecond inverting switch T₂. The second inverting node M₂ is between thesecond inverting switch T₂ and the third inverting switch T₃. The(2n−1)th inverting node M_(2n−1) is between the (2n−1)th invertingswitch T_(2n−1) and the (2n)th inverting switch T_(2n). On this basis,the (2i−1)th inverting node M_(2i−1) is between the (2i−1)th invertingswitch T_(2i-1) and the (2i)th inverting switch T_(2i), where i is aninteger larger than or equal to 2 and smaller than or equal to n.

The 2n rectifying switches D₁, D₂ to D_(2n) form n rectifyinghalf-bridge circuits sequentially. Each rectifying half-bridge circuitincludes two rectifying switches (D₁, D₂ to D_(2n)) serially connectedwith each other. One terminal of both the two rectifying switches (D₁,D₂ to D_(2n)) are electrically connected with a rectifying node (N₁, N₂to N_(n)), and the other terminal of the two rectifying switches (D₁, D₂to D_(2n)) are electrically connected with a ground terminal and theoutput terminal 12 respectively. The first rectifying node N₁ is betweenthe first rectifying switch D₁ and the second rectifying switch D₂. Thesecond rectifying node N₂ is between the third rectifying switch D₃ andthe fourth rectifying switch D₄. The (n)th rectifying node N_(n) isbetween the (2n−1)th rectifying switch D_(2n−1) and the (2n)threctifying switch D_(2n). On this basis, the (i)th rectifying node N_(i)is between the (2i−1)th rectifying switch D_(2i−1) and the (2i)threctifying switch D_(2i).

The 2n−2 clamping switches S₁, S₂ to S_(2n−2) form n−1 clampinghalf-bridge circuit(s) sequentially. Each clamping half-bridge circuitincludes two clamping switches (S₁, S₂ to S_(2n−2)) serially connectedwith each other. One terminal of both the two clamping switches (S₁, S₂to S_(2n−2)) are electrically connected with a clamping node (O₁, O₂ toO_(n)), and the other terminal of the two clamping switches (S₁, S₂ toS_(2n−2)) are electrically connected with the ground terminal and theoutput terminal 12 respectively. The first clamping node O₁ is betweenthe first clamping switch S₁ and the second clamping switch S₂. Thesecond clamping node O₂ is between the third clamping switch S₃ and thefourth clamping switch S₄. The (n−1)th clamping node O_(n-1) is betweenthe (2n−3)th clamping switch S_(2n−3) and the (2n−2)th clamping switchS_(2n−2). On this basis, the (i−1)th clamping node O_(i-1) is betweenthe (2i−3)th clamping switch S_(2i−3) and the (2i−2)th clamping switchS_(2i−2).

The resonance tank (RT₁, RT₂ to RT_(n)) is electrically connectedbetween the corresponding inverting node (M₁, M₂ to M_(2n−1)) and thecorresponding rectifying node (N₁, N₂ to N_(n)). The first resonancetank RT₁ is electrically connected between the first inverting node M₁and the first rectifying node N₁. The second resonance tank RT₂ iselectrically connected between the third inverting node M₃ and thesecond rectifying node N₂. The (n)th resonance tank RT_(n) iselectrically connected between the (2n−1)th inverting node M_(2n−1) andthe (n)th rectifying node N_(n). On this basis, the (i)th resonance tankRT₁ is electrically connected between the (2i−1)th inverting nodeM_(2i−1) and the (i)th rectifying node N_(i). In an embodiment, eachresonance tank (RT₁, RT₂ to RT_(n)) includes an inductor and a capacitorserially connected with each other. In another embodiment, eachresonance tank (RT₁, RT₂ to RT_(n)) includes an inductor or a capacitor.

The support capacitor (C₁, C₂ to C_(n-1)) is electrically connectedbetween the corresponding inverting node (M₁, M₂ to M_(2n−1)) and thecorresponding clamping node (O₁, O₂ to O_(n)). The first supportcapacitor C₁ is electrically connected between the second inverting nodeM₂ and the first clamping node O₁. The second support capacitor C₂ iselectrically connected between the fourth inverting node M₄ and thesecond clamping node O₂. The (n−1)th support capacitor C_(n-1) iselectrically connected between the (2n−2)th inverting node M_(2n−2) andthe (n−1)th clamping node O_(n-1). On this basis, the (i−1)th supportcapacitor C_(i-1) is electrically connected between the (2i−2)thinverting node M_(2i−2) and the (i−1)th clamping node O_(i-1).

In the switched-tank DC transformer 1, every support capacitor (C₁, C₂to C_(n-1)) is switchable to be in a normal state, a first voltage ratioswitching state or a second voltage ratio switching state, and everyresonance tank (RT₁, RT₂ to RT_(n)) is switchable to be in the normalstate or the second voltage ratio switching state. Accordingly, thevoltage ratio of the switched-tank DC transformer 1 is allowed to varybetween 1 and 2n. When the input voltage varies in a wide range, therange of the output voltage is limited by adjusting the voltage ratio ofthe switched-tank DC transformer 1. Therefore, both the high efficiencyof power transformation and the adjustable output voltage are achieved.According to the states of the support capacitors (C₁, C₂ to C_(n-1))and the resonance tanks (RT₁, RT₂ to RT_(n)), the operations of thenodes and switches of the switched-tank DC transformer 1 are describedin detail as follows.

When the (i−1)th support capacitor C_(i-1) is in the normal state, the(i−1)th clamping node O_(i-1) is electrically connected with the groundterminal and the output terminal 12 by turns. When the (i)th resonancetank RT_(i) is in the normal state, the (i)th rectifying node N_(i) iselectrically connected with the output terminal 12 and the groundterminal by turns. In an embodiment, when the first resonance RT_(i) isin the normal state, the first rectifying node N₁ is electricallyconnected with the output terminal 12 and the ground terminal by turns.In addition, when the (i−1)th support capacitor C_(i-1) and the (i)thresonance tank RT_(i) are both in the normal state, the (2i−2)thclamping switch S_(2i−2), the (2i−1)th inverting switch T_(2i−1) and the(2i−1)th rectifying switch D_(2i−1) are simultaneously in an ON state oran OFF state. Correspondingly, the (2i−3)th clamping switch S_(2i−3),the (2i)th inverting switch T_(2i) and the (2i)th rectifying switchD_(2i) are simultaneously in the OFF state or the ON state. In anembodiment, when the (i−1)th support capacitor C_(i-1) and the (i)thresonance tank RT_(i) are both in the normal state, the (2i−2)thclamping switch S_(2i−2) and the (2i−3)th clamping switch S_(2i−3) haveopposite switch conditions and switch on by turns. The (2i−1)thinverting switch T_(2i−1) and the (2i)th inverting switch T_(2i) haveopposite switch conditions and switch on by turns. The (2i−1)threctifying switch D_(2i−1) and the (2i)th rectifying switch D_(2i) haveopposite switch conditions and switch on by turns.

When the (i−1)th support capacitor C_(i-1) is in the first voltage ratioswitching state, the (i−1)th clamping node O_(i-1) is kept constantly inelectrical connection with the ground terminal. In an embodiment, whenthe (i−1)th support capacitor C_(i-1) is in the first voltage ratioswitching state, the (2i−2)th clamping switch S_(2i−2) is keptconstantly in the OFF state, and the (2i−3)th clamping switch S_(2i−3)is kept constantly in the ON state. Consequently, the (i−1)th clampingnode O_(i-1) is kept constantly in electrical connection with the groundterminal.

When the (i−1)th support capacitor C_(i-1) is in the second voltageratio switching state, the (i−1)th clamping node O_(i-1) is keptconstantly in an open-circuit condition, the (2i)th inverting switchT_(2i) and the (2i−2)th inverting switch T_(2i−2) are kept constantly inthe ON state, and the (2i−1)th inverting switch T_(2i−1) and the(2i−3)th inverting switch T_(2i−3) are kept constantly in the ON state.In an embodiment, when the (i−1)th support capacitor C_(i-1) is in thesecond voltage ratio switching state, the (2i−2)th clamping switchS_(2i−2) and the (2i−3)th clamping switch S_(2i−3) are kept constantlyin the OFF state. Consequently, the (i−1)th clamping node O_(i-1) iskept constantly in the open-circuit condition.

When the (i)th resonance tank RT_(i) is in the second voltage ratioswitching state, the (i)th rectifying node N_(i) is kept constantly inthe open-circuit condition, the (2i+1)th inverting switch T_(2i+1) orthe (2i−1)th inverting switch T_(2i−1) is kept constantly in the ONstate, and the (2i)th inverting switch T_(2i) or the (2i−2)th invertingswitch T_(2i-2) are kept constantly in the ON state. In an embodiment,when the (i)th resonance tank RT_(i) is in the second voltage ratioswitching state, the (2i)th rectifying switch D_(2i) and the (2i−1)threctifying switch D_(2i−1) are kept constantly in the OFF state.Consequently, the (i)th rectifying node N_(i) is kept constantly in theopen-circuit condition. In addition, when the first resonance tank RT₁is in the second voltage ratio switching state, the first rectifyingnode N₁ is kept constantly in the open-circuit condition (for example,keeping the first rectifying switch D₁ and the second rectifying switchD₂ constantly in the OFF state). The third inverting switch T₃ or thefirst inverting switch T₁ is kept constantly in the ON state. The secondinverting switch T₂ is kept constantly in the ON state. When the (n)thresonance tank RT_(n) is in the second voltage ratio switching state,the (n)th rectifying node N_(n) is kept constantly in the open-circuitcondition (for example, keeping the (2n−1)th rectifying switch D_(2n−1)and the (2n)th rectifying switch D_(2n) constantly in the OFF state).The (2n−1)th inverting switch T_(2n−1) is kept constantly in the ONstate. The (2n)th inverting switch T_(2n) or the (2n−2)th invertingswitch T_(2n−2) is kept constantly in the ON state.

Moreover, when the states of the support capacitor (C₁, C₂ to C_(n-1))and/or the resonance tank (RT₁, RT₂ to RT_(n)) are switched, the voltageratio of the switched-tank DC transformer 1 varies correspondingly. Somepossible situations are listed as follows.

When any support capacitor (C₁, C₂ to C_(n-1)) is switched from thenormal state to the first voltage ratio switching state, the voltageratio of the switched-tank DC transformer 1 is subtracted by 1. On thecontrary, when any support capacitor (C₁, C₂ to C_(n-1)) is switchedfrom the first voltage ratio switching state to the normal state, thevoltage ratio of the switched-tank DC transformer 1 is increased by 1.Since the n−1 support capacitors C₁, C₂ to C_(n-1) are all switchable tobe in the normal state or the first voltage ratio switching state, thevoltage ratio of the switched-tank DC transformer 1 is allowed to varybetween (n+1) and 2n.

When any support capacitor (C₁, C₂ to C_(n-1)) or any resonance tank(RT₁, RT₂ to RT_(n)) is switched from the normal state to the secondvoltage ratio switching state, the voltage ratio of the switched-tank DCtransformer 1 is subtracted by 2. On the contrary, when any supportcapacitor (C₁, C₂ to C_(n-1)) or any resonance tank (RT₁, RT₂ to RT_(n))is switched from the second voltage ratio switching state to the normalstate, the voltage ratio of the switched-tank DC transformer 1 isincreased by 2. Since the n−1 support capacitors C₁, C₂ to C_(n-1) andthe n resonance tanks RT₁, RT₂ to RT_(n) are all switchable to be in thenormal state or the second voltage ratio switching state, the voltageratio of the switched-tank DC transformer 1 is allowed to vary between 2and 2n.

When A support capacitor(s) (C₁, C₂ to C_(n-1)) is/are switched from thenormal state to the first voltage ratio switching state, and B resonancetank(s) (RT₁, RT₂ to RT_(n)) is/are switched from the normal state tothe second voltage ratio switching state, the voltage ratio of theswitched-tank DC transformer 1 is subtracted by A+2B. On the contrary,when A support capacitor(s) (C₁, C₂ to C_(n-1)) is/are switched from thefirst voltage ratio switching state to the normal state, and B resonancetank(s) (RT₁, RT₂ to RT_(n)) is/are switched from the second voltageratio switching state to the normal state, the voltage ratio of theswitched-tank DC transformer 1 is increased by A+2B. A is a naturalnumber smaller than or equal to n−1, and B is a natural number smallerthan or equal to n. Since the n−1 support capacitors C₁, C₂ to C_(n-1)are switchable to be in the normal state or the first voltage ratioswitching state, and the n resonance tanks RT₁, RT₂ to RT_(n) areswitchable to be in the normal state or the second voltage ratioswitching state, the voltage ratio of the switched-tank DC transformer 1is allowed to vary between 1 and 2n.

When A support capacitor(s) (C₁, C₂ to C_(n-1)) and B resonance tank(s)(RT₁, RT₂ to RT_(n)) are switched from the normal state to the secondvoltage ratio switching state, the voltage ratio of the switched-tank DCtransformer 1 is subtracted by 2A+2B. On the contrary, when A supportcapacitor(s) (C₁, C₂ to C_(n-1)) and B resonance tank(s) (RT₁, RT₂ toRT_(n)) are switched from the second voltage ratio switching state tothe normal state, the voltage ratio of the switched-tank DC transformer1 is increased by 2A+2B. Since the n−1 support capacitors C₁, C₂ toC_(n-1) and the n resonance tanks RT₁, RT₂ to RT_(n) are switchable tobe in the normal state or the second voltage ratio switching state, thevoltage ratio of the switched-tank DC transformer 1 is allowed to varybetween 2 and 2n.

In order to be understood more easily, the switched-tank DC transformer1 with n equal to 2 is shown as an example, but the switched-tank DCtransformer of the present disclosure is not limited thereto. FIG. 2A isa schematic circuit diagram illustrating the switched-tank DCtransformer of FIG. 1 with n equal to 2. FIGS. 2B and 2C are schematicdiagrams showing the different switch conditions of the switched-tank DCtransformer of FIG. 2A. As shown in FIG. 2A, in this embodiment, nequals 2, and the switched-tank DC transformer 1 includes an inputterminal 11, an output terminal 12, four inverting switches T₁, T₂, T₃,T₄, four rectifying switches D₁, D₂, D₃, D₄, two clamping switches S₁,S₂, two resonance tanks RT₁, RT₂ and one support capacitor C₁. As shownin the schematic diagrams of different switch conditions (see FIGS. 2Band 2C), the part of the circuit that the current not passing through isdepicted by relatively thin lines. Therefore, the current path underdifferent switch conditions can be recognized and distinguished. Asshown in FIGS. 2B and 2C, when the support capacitor C₁ and theresonance tanks RT₁, RT₂ are all in the normal state, the first clampingswitch S₁, the second inverting switch T₂, the fourth inverting switchT₄, the second rectifying switch D₂ and the fourth rectifying switch D₄are simultaneously in the ON state or the OFF state. Correspondingly,the second clamping switch S₂, the first inverting switch T₁, the thirdinverting switch T₃, the first rectifying switch D₁ and the thirdrectifying switch D₃ are simultaneously in the OFF state or the ONstate. In particular, the first clamping switch S₁ and the secondclamping switch S₂ have opposite switch conditions and switch on byturns. The first inverting switch T₁ and the second inverting switch T₂have opposite switch conditions and switch on by turns. The thirdinverting switch T₃ and the fourth inverting switch T₄ have oppositeswitch conditions and switch on by turns. The first rectifying switch D₁and the second rectifying switch D₂ have opposite switch conditions andswitch on by turns. The third rectifying switch D₃ and the fourthrectifying switch D₄ have opposite switch conditions and switch on byturns.

In this embodiment, by switching the states of the support capacitor C₁and the resonance tanks RT₁, RT₂, the voltage ratio of the switched-tankDC transformer 1 is allowed to vary between 1 and 4. Some specificexamples are shown as follows. However, in the actual applications, theway of switching the states of the support capacitor C₁ and theresonance tanks RT₁, RT₂ is not limited thereto.

Under the circumstance that the first support capacitor C₁ is switchedfrom the normal state to the first voltage ratio switching state, andthe resonance tanks RT₁, RT₂ are in the normal state. As shown in FIG.3A, the first clamping switch S₁ is kept constantly in the ON state, thesecond clamping switch S₂ is kept constantly in the OFF state, thus thefirst clamping node O₁ is kept constantly in electrical connection withthe ground terminal. The two different switch conditions are shown inFIGS. 3B and 3C. The voltage ratio of the switched-tank DC transformer 1equals 3. Under this circumstance, the voltage ratio is reduced by 1 ascompared with the voltage ratio of the switched-tank DC transformer 1 ofFIG. 2A.

Under the circumstance that the first support capacitor C₁ is switchedfrom the normal state to the second voltage ratio switching state, andthe resonance tanks RT₁, RT₂ are in the normal state. As shown in FIG.4A, the first clamping switch S₁ and the second clamping switch S₂ arekept constantly in the OFF state, thus the first clamping node O₁ iskept constantly in the open-circuit condition. The second invertingswitch T₂ and the third inverting switch T₃ are kept constantly in theON state. The two different switch conditions are shown in FIGS. 4B and4C. The voltage ratio of the switched-tank DC transformer 1 equals 2.Under this circumstance, the voltage ratio is reduced by 2 as comparedwith the voltage ratio of the switched-tank DC transformer 1 of FIG. 2A.Alternatively, in an embodiment, the first resonance tank RT₁ or thesecond resonance tank RT₂ is switched from the normal state to thesecond voltage ratio switching state, so as to make the voltage ratio ofthe switched-tank DC transformer 1 equal to 2.

Under the circumstance that the first support capacitor C₁ is switchedfrom the normal state to the first voltage ratio switching state, andthe second resonance tank RT₂ is switched from the normal state to thesecond voltage ratio switching state. As shown in FIG. 5A, the firstclamping switch S₁ is kept constantly in the ON state, the secondclamping switch S₂ is kept constantly in the OFF state, thus the firstclamping node O₁ is kept constantly in electrical connection with theground terminal. The third rectifying switch D₃ and the fourthrectifying switch D₄ are kept constantly in the OFF state, thus thesecond rectifying node N₂ is kept constantly in the open-circuitcondition. The third inverting switch T₃ and the fourth inverting switchT₄ are kept constantly in the ON state. The two different switchconditions are shown in FIGS. 5B and 5C. The voltage ratio of theswitched-tank DC transformer 1 equals 1. Under this circumstance, thevoltage ratio is reduced by 3 as compared with the voltage ratio of theswitched-tank DC transformer 1 of FIG. 2A. Alternatively, in anembodiment, the first support capacitor C₁ is switched from the normalstate to the first voltage ratio switching state, and the firstresonance tank RT₁ is switched from the normal state to the secondvoltage ratio switching state, so as to make the voltage ratio of theswitched-tank DC transformer 1 equal to 1.

FIG. 6 is a flowchart illustrating a voltage ratio switching methodaccording an embodiment of the present disclosure. The voltage ratioswitching method is applied to the switched-tank DC transformer 1 ofFIG. 1. The voltage ratio switching method controls the switchconditions of the support capacitors (C₁, C₂ to C_(n-1)) and theresonance tanks (RT₁, RT₂ to RT_(n)), and further adjusts the voltageratio of the switched-tank DC transformer 1. The voltage ratio switchingmethod includes the following steps S1, S2, S3, S4 and S5.

Step S1: Controlling the (i−1)th support capacitor C_(i-1) to be in thenormal state, namely controlling the (i−1)th clamping node O_(i-1) toelectrically connect the ground terminal and the output terminal 12 byturns.

Step S2: Controlling the (i−1)th support capacitor C_(i-1) to be in thefirst voltage ratio switching state, namely controlling the (i−1)thclamping node O_(i-1) to be constantly in electrical connection with theground terminal. In an embodiment, the (2i−2)th clamping switch S_(2i−2)is controlled to be constantly in the OFF state, and the (2i−3)thclamping switch S_(2i−3) is controlled to be constantly in the ON state.

Step S3: Controlling the (i−1)th support capacitor C_(i-1) to be in thesecond voltage ratio switching state, namely controlling the (i−1)thclamping node O_(i-1) to be constantly in the open-circuit condition,controlling the (2i)th inverting switch T_(2i) or the (2i−2)th invertingswitch T_(2i-2) to be constantly in the ON state, and controlling the(2i−1)th inverting switch T_(2i−1) or the (2i−3)th inverting switchT_(2i−3) to be constantly in the ON state. In an embodiment, the(2i−2)th clamping switch S_(2i−2) and the (2i−3)th clamping switchS_(2i−3) are controlled to be constantly in the OFF state, thus the(i−1)th clamping node O_(i-1) is kept constantly in the open-circuitcondition.

Step S4: Controlling the (i)th resonance tank RT_(i) to be in the normalstate, namely controlling the (i)th rectifying node N_(i) toelectrically connect the output terminal 12 and the ground terminal byturns.

Step S5: Controlling the (i)th resonance tank RT_(i) to be in the secondvoltage ratio switching state, namely controlling the (i)th rectifyingnode N_(i) to be constantly in the open-circuit condition, controllingthe (2i+1)th inverting switch T_(2i+1) or the (2i−1)th inverting switchT_(2i−1) to be constantly in the ON state, and controlling the (2i)thinverting switch T_(2i) or the (2i−2)th inverting switch T_(2i-2) to beconstantly in the ON state. In an embodiment, the (2i)th rectifyingswitch D_(2i) and the (2i−1)th rectifying switch D_(2i−1) are controlledto be constantly in the OFF state, thus the (i)th rectifying node N_(i)is kept constantly in the open-circuit condition.

In an embodiment, the step S4 further includes a step of controlling thefirst resonance tank RT₁ to be in the normal state, namely the firstrectifying node N_(i) is controlled to electrically connect the outputterminal 12 and the ground terminal by turns. In an embodiment, the stepS5 further includes a step of controlling the first resonance tank RT₁to be in the second voltage ratio switching state. Namely, the firstrectifying node N₁ is controlled to be constantly in the open-circuitcondition (for example, controlling the second rectifying switch D₂ andthe first rectifying switch D₁ to be constantly in the OFF state). Thethird inverting switch T₃ or the first inverting switch T₁ is controlledto be constantly in the ON state. The second inverting switch T₂ iscontrolled to be constantly in the ON state.

It is noted that FIG. 6 only shows the steps included by the voltageratio switching method. There is no order relationship among the stepsS1, S2, S3, S4 and S5. One or plural of the steps can be performed inany order according to the actual requirements, and meanwhile the numberof steps performed is not limited. Moreover, the above steps can beperformed to one or plural support capacitor(s) (C₁, C₂ to C_(n-1))and/or one or plural resonance tank(s) (RT₁, RT₂ to RT_(n)). Inaddition, while the step(s) is/are performed, the effect on the voltageratio of the switched-tank DC transformer 1 is described as follows.

After the step S1 is performed to any support capacitor (C₁, C₂ toC_(n-1)), if the step S2 is performed to that support capacitor (C₁, C₂to C_(n-1)), the voltage ratio of the switched-tank DC transformer 1 issubtracted by 1. On the contrary, after the step S2 is performed to anysupport capacitor (C₁, C₂ to C_(n-1)), if the step S1 is performed tothat support capacitor (C₁, C₂ to C_(n-1)), the voltage ratio of theswitched-tank DC transformer 1 is increased by 1. Since the n−1 supportcapacitors C₁, C₂ to C_(n-1) can be switched between the normal stateand the first voltage ratio switching state by the voltage ratioswitching method, the voltage ratio of the switched-tank DC transformer1 is allowed to vary between n+1 and 2n.

After the step S1 is performed to any support capacitor (C₁, C₂ toC_(n-1)), if the step S3 is performed to that support capacitor (C₁, C₂to C_(n-1)), the voltage ratio of the switched-tank DC transformer 1 issubtracted by 2. On the contrary, after the step S3 is performed to anysupport capacitor (C₁, C₂ to C_(n-1)), if the step S1 is performed tothat support capacitor (C₁, C₂ to C_(n-1)), the voltage ratio of theswitched-tank DC transformer 1 is increased by 2. Since the n−1 supportcapacitors C₁, C₂ to C_(n-1) can be switched between the normal stateand the second voltage ratio switching state by the voltage ratioswitching method, the voltage ratio of the switched-tank DC transformer1 is allowed to vary between 2 and 2n.

After the step S4 is performed to any resonance tank (RT₁, RT₂ toRT_(n)), if the step S5 is performed to that resonance tank (RT₁, RT₂ toRT_(n)), the voltage ratio of the switched-tank DC transformer 1 issubtracted by 2. On the contrary, after the step S5 is performed to anyresonance tank (RT₁, RT₂ to RT_(n)), if the step S4 is performed to thatresonance tank (RT₁, RT₂ to RT_(n)), the voltage ratio of theswitched-tank DC transformer 1 is increased by 2. Since the n resonancetanks RT₁, RT₂ to RT_(n) can be switched between the normal state andthe second voltage ratio switching state by the voltage ratio switchingmethod, the voltage ratio of the switched-tank DC transformer 1 isallowed to vary between 2 and 2n.

After the steps S1 and S4 are performed to A support capacitor(s) (C₁,C₂ to C_(n-1)) and B resonance tank(s) (RT₁, RT₂ to RT_(n))respectively, if the steps S3 and S5 are performed to the A supportcapacitor(s) (C₁, C₂ to C_(n-1)) and the B resonance tank(s) (RT₁, RT₂to RT_(n)) respectively, the voltage ratio of the switched-tank DCtransformer 1 is subtracted by 2A+2B. On the contrary, after the stepsS3 and S5 are performed to A support capacitor(s) (C₁, C₂ to C_(n-1))and B resonance tank(s) (RT₁, RT₂ to RT_(n)) respectively, if the stepsS1 and S4 are performed to the A support capacitor(s) (C₁, C₂ toC_(n-1)) and the B resonance tank(s) (RT₁, RT₂ to RT_(n)) respectively,the voltage ratio of the switched-tank DC transformer 1 is increased by2A+2B. A is a natural number smaller than or equal to n−1, and B is anatural number smaller than or equal to n. Since the n−1 supportcapacitors C₁, C₂ to C_(n-1) and the n resonance tanks RT₁, RT₂ toRT_(n) can be switched between the normal state and the second voltageratio switching state by the voltage ratio switching method, the voltageratio of the switched-tank DC transformer 1 is allowed to vary between 2and 2n.

After the steps S1 and S4 are performed to A support capacitor(s) (C₁,C₂ to C_(n-1)) and B resonance tank(s) (RT₁, RT₂ to RT_(n))respectively, if the steps S2 and S5 are performed to the A supportcapacitor(s) (C₁, C₂ to C_(n-1)) and the B resonance tank(s) (RT₁, RT₂to RT_(n)) respectively, the voltage ratio of the switched-tank DCtransformer 1 is subtracted by A+2B. On the contrary, after the steps S2and S5 are performed to A support capacitor(s) (C₁, C₂ to C_(n-1)) and Bresonance tank(s) (RT₁, RT₂ to RT_(n)) respectively, if the steps S1 andS4 are performed to the A support capacitor(s) (C₁, C₂ to C_(n-1)) andthe B resonance tank(s) (RT₁, RT₂ to RT_(n)) respectively, the voltageratio of the switched-tank DC transformer 1 is increased by A+2B. Sincethe n−1 support capacitors C₁, C₂ to C_(n-1) and the n resonance tanksRT₁, RT₂ to RT_(n) can be switched between the normal state and thefirst voltage ratio switching state by the voltage ratio switchingmethod, the voltage ratio of the switched-tank DC transformer 1 isallowed to vary between 1 and 2n.

From the above descriptions, the present disclosure provides aswitched-tank DC transformer and a voltage ratio switching methodthereof. In the switched-tank DC transformer, every support capacitorand every resonance tank is switchable to be in a normal state or avoltage ratio switching state. Accordingly, the voltage ratio of theswitched-tank DC transformer is changed at will. When the input voltagevaries in a wide range, the range of the output voltage can be limitedby adjusting the voltage ratio of the switched-tank DC transformer.Therefore, both the high efficiency of power transformation and theadjustable output voltage are achieved. Moreover, with regard to thevoltage regulator module including the switched-tank DC transformer, theefficiency and quality of supplying power thereof are enhanced.

While the disclosure has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the disclosure needs not be limited to the disclosedembodiment. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

What is claimed is:
 1. A switched-tank DC transformer, comprising: an input terminal and an output terminal; 2n inverting switches serially connected to form n inverting half-bridge circuits, wherein n is an integer larger than or equal to 2, the first inverting switch is electrically connected with the output terminal, the (2n)th inverting switch is electrically connected with the input terminal, there is an inverting node between every two neighboring inverting switches, the (2i−1)th inverting node is between the (2i)th inverting switch and the (2i−1)th inverting switch, and i is an integer larger than or equal to 2 and smaller than or equal to n; 2n rectifying switches forming n rectifying half-bridge circuits sequentially, wherein each of the n rectifying half-bridge circuits comprises two rectifying switches serially connected with each other, one terminal of both the two rectifying switches are electrically connected with a rectifying node, the other terminal of the two rectifying switches are electrically connected with a ground terminal and the output terminal respectively, and the (i)th rectifying node is between the (2i)th rectifying switch and the (2i−1)th rectifying switch; 2n−2 clamping switches forming n−1 clamping half-bridge circuits sequentially, wherein each of the n−1 clamping half-bridge circuits comprises two clamping switches serially connected with each other, one terminal of both the two clamping switches are electrically connected with a clamping node, the other terminal of the two clamping switches are electrically connected with the ground terminal and the output terminal respectively, and the (i−1)th clamping node is between the (2i−2)th clamping switch and the (2i−3)th clamping switch; n resonance tanks, wherein the resonance tank is electrically connected between the corresponding inverting node and the corresponding rectifying node, and the (i)th resonance tank is electrically connected between the (2i−1)th inverting node and the (i)th rectifying node; and n−1 support capacitors, wherein the support capacitor is electrically connected between the corresponding inverting node and the corresponding clamping node, and the (i−1)th support capacitor is electrically connected between the (2i−2)th inverting node and the (i−1)th clamping node, wherein each of the n−1 support capacitors is switchable to be in a normal state or a voltage ratio switching state, each of the n resonance tanks is switchable to be in the normal state or the voltage ratio switching state, thus a voltage ratio of the switched-tank DC transformer varies between 2 and 2n, when the (i−1)th support capacitor is in the normal state, the (i−1)th clamping node is electrically connected with the ground terminal and the output terminal by turns; when the (i−1)th support capacitor is in the voltage ratio switching state, the (i−1)th clamping node is kept constantly in an open-circuit condition, the (2i)th inverting switch or the (2i−2)th inverting switch is kept constantly in an ON state, the (2i−1)th inverting switch or the (2i−3)th inverting switch is kept constantly in the ON state, when the (i)th resonance tank is in the normal state, the (i)th rectifying node is electrically connected with the output terminal and the ground terminal by turns; when the (i)th resonance tank is in the voltage ratio switching state, the (i)th rectifying node is kept constantly in the open-circuit condition, the (2i+1)th inverting switch or the (2i−1)th inverting switch is kept constantly in the ON state, the (2i)th inverting switch or the (2i−2)th inverting switch is kept constantly in the ON state.
 2. The switched-tank DC transformer according to claim 1, wherein when the first resonance tank is in the normal state, the first rectifying node is electrically connected with the output terminal and the ground terminal by turns; wherein when the first resonance tank is in the voltage ratio switching state, the first rectifying node is kept constantly in the open-circuit condition, the third inverting switch or the first inverting switch is kept constantly in the ON state, and the second inverting switch is kept constantly in the ON state.
 3. The switched-tank DC transformer according to claim 1, wherein when the (i−1)th support capacitor and the (i)th resonance tank are both in the normal state, the (2i−2)th clamping switch, the (2i−1)th inverting switch and the (2i−1)th rectifying switch are simultaneously in the ON state or an OFF state, and the (2i−3)th clamping switch, the (2i)th inverting switch and the (2i)th rectifying switch are simultaneously in the OFF state or the ON state correspondingly.
 4. The switched-tank DC transformer according to claim 3, wherein when the (i−1)th support capacitor and the (i)th resonance tank are both in the normal state, the (2i−2)th clamping switch and the (2i−3)th clamping switch have opposite switch conditions and switch on by turns; the (2i−1)th inverting switch and the (2i)th inverting switch have opposite switch conditions and switch on by turns; and the (2i−1)th rectifying switch and the (2i)th rectifying switch have opposite switch conditions and switch on by turns.
 5. The switched-tank DC transformer according to claim 1, wherein when the (i−1)th support capacitor is in the voltage ratio switching state, the (2i−2)th clamping switch and the (2i−3)th clamping switch are kept constantly in an OFF state, the (2i)th inverting switch or the (2i−2)th inverting switch is kept constantly in the ON state, and the (2i−1)th inverting switch or the (2i−3)th inverting switch is kept constantly in the ON state.
 6. The switched-tank DC transformer according to claim 1, wherein when the (i)th resonance tank is in the voltage ratio switching state, the (2i)th rectifying switch and the (2i−1)th rectifying switch are kept constantly in an OFF state, the (2i+1)th inverting switch or the (2i−1)th inverting switch is kept constantly in the ON state, and the (2i)th inverting switch or the (2i−2)th inverting switch is kept constantly in the ON state.
 7. The switched-tank DC transformer according to claim 1, wherein when the first resonance tank is in the voltage ratio switching state, the second rectifying switch and the first rectifying switch are kept constantly in an OFF state, the third inverting switch or the first inverting switch is kept constantly in the ON state, and the second inverting switch is kept constantly in the ON state.
 8. The switched-tank DC transformer according to claim 1, wherein when any of the support capacitors or any of the resonance tanks is switched from the normal state to the voltage ratio switching state, the voltage ratio of the switched-tank DC transformer is subtracted by 2, and when any of the support capacitors or any of the resonance tanks is switched from the voltage ratio switching state to the normal state, the voltage ratio of the switched-tank DC transformer is increased by
 2. 9. The switched-tank DC transformer according to claim 1, wherein when A support capacitor(s) and B resonance tank(s) are switched from the normal state to the voltage ratio switching state, the voltage ratio of the switched-tank DC transformer is subtracted by 2A+2B, when A support capacitor(s) and B resonance tank(s) are switched from the voltage ratio switching state to the normal state, the voltage ratio of the switched-tank DC transformer is increased by 2A+2B, and A is a natural number smaller than or equal to n−1, B is a natural number smaller than or equal to n.
 10. The switched-tank DC transformer according to claim 1, wherein each of the resonance tanks comprises an inductor or a capacitor or each of the resonance tanks comprises an inductor and a capacitor serially connected with each other.
 11. A voltage ratio switching method of a switched-tank DC transformer, wherein the switched-tank DC transformer comprises an input terminal, an output terminal, 2n inverting switches, 2n rectifying switches, 2n−2 clamping switches, n resonance tanks and n−1 support capacitors, n is an integer larger than or equal to 2, the 2n inverting switches are serially connected to form n inverting half-bridge circuits, the first inverting switch is electrically connected with the output terminal, the (2n)th inverting switch is electrically connected with the input terminal, there is an inverting node between every two neighboring inverting switches, the (2i−1)th inverting node is between the (2i)th inverting switch and the (2i−1)th inverting switch, and i is an integer larger than or equal to 2 and smaller than or equal to n; the 2n rectifying switches form n rectifying half-bridge circuits sequentially, each of the n rectifying half-bridge circuits comprises two rectifying switches serially connected with each other, one terminal of both the two rectifying switches are electrically connected with a rectifying node, the other terminal of the two rectifying switches are electrically connected with a ground terminal and the output terminal respectively, and the (i)th rectifying node is between the (2i)th rectifying switch and the (2i−1)th rectifying switch; the 2n−2 clamping switches form n−1 clamping half-bridge circuits sequentially, each of the n−1 clamping half-bridge circuits comprises two clamping switches serially connected with each other, one terminal of both the two clamping switches are electrically connected with a clamping node, the other terminal of the two clamping switches are electrically connected with the ground terminal and the output terminal respectively, and the (i−1)th clamping node is between the (2i−2)th clamping switch and the (2i−3)th clamping switch; the resonance tank is electrically connected between the corresponding inverting node and the corresponding rectifying node, and the (i)th resonance tank is electrically connected between the (2i−1)th inverting node and the (i)th rectifying node; and the support capacitor is electrically connected between the corresponding inverting node and the corresponding clamping node, and the (i−1)th support capacitor is electrically connected between the (2i−2)th inverting node and the (i−1)th clamping node, the voltage ratio switching method controlling every support capacitor to be switchably in a normal state or a voltage ratio switching state, the voltage ratio switching method controlling every resonance tank to be switchably in the normal state or the voltage ratio switching state, the voltage ratio switching method allowing a voltage ratio of the switched-tank DC transformer to vary between 2 and 2n, the voltage ratio switching method comprising: (a) controlling the (i−1)th support capacitor to be in the normal state, namely controlling the (i−1)th clamping node to electrically connect the ground terminal and the output terminal by turns; (b) controlling the (i−1)th support capacitor to be in the voltage ratio switching state, namely controlling the (i−1)th clamping node to be constantly in an open-circuit condition, controlling the (2i)th inverting switch or the (2i−2)th inverting switch to be constantly in an ON state, and controlling the (2i−1)th inverting switch or the (2i−3)th inverting switch to be constantly in the ON state; (c) controlling the (i)th resonance tank to be in the normal state, namely controlling the (i)th rectifying node to electrically connect the output terminal and the ground terminal by turns; and (d) controlling the (i)th resonance tank to be in the voltage ratio switching state, namely controlling the (i)th rectifying node to be constantly in the open-circuit condition, controlling the (2i+1)th inverting switch or the (2i−1)th inverting switch to be constantly in the ON state, and controlling the (2i)th inverting switch or the (2i−2)th inverting switch to be constantly in the ON state.
 12. The voltage ratio switching method according to claim 11, wherein the step (c) further comprises a step of controlling the first resonance tank to be in the normal state, namely the first rectifying node is controlled to electrically connect the output terminal and the ground terminal by turns; and wherein the step (d) further comprises a step of controlling the first resonance tank to be in the voltage ratio switching state, namely, the first rectifying node is controlled to be constantly in the open-circuit condition, the third inverting switch or the first inverting switch is controlled to be constantly in the ON state, and the second inverting switch is controlled to be constantly in the ON state.
 13. The voltage ratio switching method according to claim 11, wherein when the (i−1)th support capacitor and the (i)th resonance tank are both in the normal state, the (2i−2)th clamping switch, the (2i−1)th inverting switch and the (2i−1)th rectifying switch are simultaneously in the ON state or an OFF state, and the (2i−3)th clamping switch, the (2i)th inverting switch and the (2i)th rectifying switch are simultaneously in the OFF state or the ON state correspondingly.
 14. The voltage ratio switching method according to claim 11, wherein when the (i−1)th support capacitor and the (i)th resonance tank are both in the normal state, the (2i−2)th clamping switch and the (2i−3)th clamping switch have opposite switch conditions and switch on by turns; the (2i−1)th inverting switch and the (2i)th inverting switch have opposite switch conditions and switch on by turns; and the (2i−1)th rectifying switch and the (2i)th rectifying switch have opposite switch conditions and switch on by turns.
 15. The voltage ratio switching method according to claim 11, wherein in the step (b), the (2i−2)th clamping switch and the (2i−3)th clamping switch are controlled to be constantly in an OFF state, the (2i)th inverting switch or the (2i−2)th inverting switch is controlled to be constantly in the ON state, and the (2i−1)th inverting switch or the (2i−3)th inverting switch is controlled to be constantly in the ON state.
 16. The voltage ratio switching method according to claim 11, wherein in the step (d), the (2i)th rectifying switch and the (2i−1)th rectifying switch are controlled to be constantly in an OFF state, the (2i+1)th inverting switch or the (2i−1)th inverting switch is controlled to be constantly in the ON state, and the (2i)th inverting switch or the (2i−2)th inverting switch is controlled to be constantly in the ON state.
 17. The voltage ratio switching method according to claim 11, wherein the step (d) further comprises: controlling the second rectifying switch and the first rectifying switch to be constantly in an OFF state, controlling the third inverting switch or the first inverting switch to be constantly in the ON state, and controlling the second inverting switch to be constantly in the ON state.
 18. The voltage ratio switching method according to claim 11, wherein after performing the step (a) to any of the support capacitors, if the step (b) is performed to that support capacitor, the voltage ratio of the switched-tank DC transformer is subtracted by 2, and wherein after performing the step (b) to any of the support capacitors, if the step (a) is performed to that support capacitor, the voltage ratio of the switched-tank DC transformer is increased by
 2. 19. The voltage ratio switching method according to claim 11, wherein after performing the step (c) to any of the resonance tanks, if the step (d) is performed to that resonance tank, the voltage ratio of the switched-tank DC transformer is subtracted by 2, and wherein after performing the step (d) to any of the resonance tanks, if the step (c) is performed to that resonance tank, the voltage ratio of the switched-tank DC transformer is increased by
 2. 20. The voltage ratio switching method according to claim 11, wherein after performing the steps (a) and (c) to A support capacitor(s) and B resonance tank(s) respectively, if the steps (b) and (d) are performed to the A support capacitor(s) and the B resonance tank(s) respectively, the voltage ratio of the switched-tank DC transformer is subtracted by 2A+2B, wherein after performing the steps (b) and (d) to A support capacitor(s) and B resonance tank(s) respectively, if the steps (a) and (c) are performed to the A support capacitor(s) and the B resonance tank(s) respectively, the voltage ratio of the switched-tank DC transformer is increased by 2A+2B, and A is a natural number smaller than or equal to n−1, B is a natural number smaller than or equal to n. 